Telephone-exchange system.



No. 679,788. Patented Aug. 6, l90l.

n. smcLAma w. AITKEN.

TELEPHONE EXCHANGE SYSTEM.

(Application filed Dec. 29, 1897.)

(No Model.)

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UNITED STATES PATENT OFFICE.

DANIEL SINCLAIR AND WILLIAM AITKEN, OF LONDON, ENGLAND, ASSIGNORS TO WESTERN ELECTRIC COMPANY, OF CHICAGO, ILLINOIS.

TELEPHONE-EXCHANGE SYSTEM.

SPECIFICATION forming part of Letters Patent No. 679,788, dated August 6, 1901. Application filed December 29, 1897. Serial No. 664.345. (No model.)

To all whom, it may concern.-

Be it known that we, DANIEL SINCLAIR, engineer-in-chicf to the National Telephone Company, Limited, Oxford Court, Cannon street, in the city of London, England, and

WILLIAM AITKEN, engineer with said company, at above address, have invented a certain new and useful Central-Battery Telephone-EXchange System, (which has been pat- 1o ented in Great Britain by Letters Patent,

dated June 25, 1896, No. 14,064,) of which the following is a specification.

Our invention concerns signals associated with telephone lines in telephone switchboards for indicating calls sent in the lines signals and improved modes of operating the same for calling for connection and discon I nection.

To this end it consists in a line-signal and means for disclosing it to indicate a call, a

2 5 clearing-out signal associated with link conductors for uniting lines, and means for bringing it into operative connection with the lines to signal for disconnection, and means for efiacing the line-signal and rendering it 0 inoperative when the clearing-out signal is,

brought into connection with the united lines.

In telephone-exchange systems it is customary to provide at each substation a switch for supporting the telephone, constructed to 5 change its position when relieved of the weight of the telephone during the use of this instrument, in connection with circuits which are changed by the said switch to shift the circuits for various purposes, and it is further 0 usual to associate with the telephone-line in a switchboard spring-jacks for making connection with the line, and a signal responsive to currents in the line, which are determined by the position of the before-mentioned switch at the substation, link conductors for uniting lines by means of their spring-jacks, and a clearing-out signal or equivalent appliance associated with the link conductors and also responsive to currents in both of the lines united by means of the link conductors, as

such current are determined by the operation of the switches. In such systemsit is essen tial that the special line-signal shall be rendered inoperative when connection is made with the line in order to avoid misleading signals in the switchboard, and it is further desirable that the clearing-out signal shall be hidden at all times except during the disuse of thesubstation-telephones oflines united for conversation.

Our invention applies to switching systems of this general arrangement and is addressed to the requirements mentioned.

It consists in, first, the combination, with the telephone-switch at the substation, of a bridge of the line and a ground connection therefrom closed by the switch when the telephone is not in use, together with a bridge of the line at a central office, a ground branch from the bridge, and asignal and a source of current in the branch, the signal being constructed to be hidden while excited by current in the normally complete circuit, thus formed; second, in a bridge of the plug-circuit or link conductor, a ground branch from this bridge, a clearing-out signal in a ground branch, the signal also being constructed to display its indicator when inert; third, alocal circuit for the clearing-out signal controlled through the agency of a terminal plug of the plug-circuit when not in use, whereby the clearing-out signal is hidden while the plugcircuit is idle, and, fourth, circuit connections adapted to bring the clearing-out signal and the line-signals of united lines, together with the sources of current in circuit with the line-signals, into a complete circuit, whereby all the signals are excited during connection between the lines while the telephones thereof are in use, together with means for shunting the clearing-out signal to cause its display when the telephones are replaced on their switches.

Our invention is illustrated in the attached diagram, which represents two substations connected by line-circuits, each with a springjack and a signal in a telephone-switchboard, together with a pair of plugs and a plug-circuit and their associated keys and clearingout signal in the switchboard.

The apparatus at the substation comprises a receiving-telephone a and a transmittingtelephone a a call-bell a and a telephoneswitch a. Line conductors 1 and 2 are united at the substation by two bridges 3 and 4:,whose continuity is controlled by the telephoneswitch a. The latter branch includes the magnet-windings of the call-bell a and is normally closed at the switch-contacts of the telephone-switch, while the former branch,

including the telephones a and a is normally open at other contact-pieces of the switch. When the switch is relieved from the weight of the telephone, it is designed to rise and open the circuit through the bell, while closing that through the telephones. The switch is associated with other contactpieces a at, which control the continuity of a ground branch 5 from the middle point of the windings of hell a being adapted to complete this conductor when the telephone rests on the switch. Stations A and A are similarly equipped. furnished with a suitable source of current for exciting the transmitting-telephone, together withthe necessary and well-known circuits and switches for controlling the current therefrom. Such parts have been omit ted in order to avoid confusing the drawings. Line conductors 1 and 2 from these appliances at the substation are led to the terminals of a spring-jack b, which is located in a telephone-switchboard, and are further extended to be united through the windings of an impedance-coil c. From the middleof this impedance-coil a branch 6 is led to the ground, in which an individual line-signald is interposed, together with a battery 6 or other source of current. The signal at is designed to retain its indicator in a concealed position while its magnet is excited, permitting the display of its signal only when the magnet becomes inert. The attendant at the switchboard is provided with pairs of plugs 'fand f and plug-circuits uniting the plugs for the purpose of linking lines together. The plugs are constructed with contact-pieces adapted to register with the contact parts of the spring-jacks I). Like contact-pieces of the two plugs which constitute a pair are united by conductors 7 and 8, which make upthe circuit which we designate the plugcircuit. The conductors of this plug-circuit include the switch-contacts of the usual call.- ing-key g for disconnecting plug f from its mate and looping it into circuit with a generator of callin g-current and the operators listening-key h for bringing her telephone into connection with the plug-circuit. A clearing-out signal 1' is associated with the plug-circuit in a ground branch 9 from the central point of a conductor lO,which forms a bridge of the plugcircuit. An impedance-coil k, with two windings, has a winding interposed between each conductor of the plug-circuit and the point of junction of conductor 9 with the bridge 10 to prevent the shunting of telephonic current through the bridge. The signal 7 like the linesignal d, is designed to display its indicator It is assumed that each isonly when its magnet is inert. its magnet should be of high resistance, twenty-five hundred ohms being sufficient. A locally-closed circuit is provided for this clearing-out signal to maintain its concealed condition during the idleness of the plugs, consisting in a conductor 11, leading from the conductor 9, between the signal 1' and the bridge 10, to the free pole of battery 6. The continuity of this local circuit is controlled, however, by the contact-points of a switch Z, located in the seat of plug f, the switch being adapted to complete the circuit when the plug is in its seat. A resistance-coil m is interposed in this conductor 11 to prevent waste of current in the local circuit.

The normal conditions of the various appliances are as follows: The telephones at the substations rest on the switches a whereby the circuits through the telephones are broken, those through the call-bells being closed, and the ground branches 5 from the lines are complete, permitting current to flow from battery 6 in the central office to excite the signals d of the lines. These signals are accordingly concealed from View. Plugs f andf rest in their sockets, whereby a current is permitted to flow through conductors 9 and 11, which excites the magnet of signal 11 and keeps the target thereof hidden. The

removal of thetelephone from its switch at either station for use automatically permits the switch to break the conductor 5, whereby the current from battery e is interrupted time bringing her telephone into connection with the plug-circuit by means of key h. The act of raising the plug from its seat breaks the conductor 11 and permits the target of the clearing-out signal to come into view. The operator attaches no importance to this signal. The insertion of the plug into the spring-jack brings about a new arrangement of the circuits, including the line-signal of the calling-line and the clearing-out signal associated with the plug used, whereby both signals are concealed, as follows: Current from battery 6 finds circuit through the conductor 6, thence to line conductors 1 and 2, thence to the contact-pieces of the springjack 1) and to the corresponding parts of plug f registering therewith, thence through portions of the conductors 7 and 8 of the plugcircuit, through the bridge 10, and thence through conductor 9 to earth. Inasmuch as line-signal d and clearing-out signal dare included in the circuit thus formed, the magnets of bothsignals become excited and effect the concealment of the targets which they control. Having learned the order of the calling-subscriber for the required connection, the operator inserts plug f in the spring-jack b of the line called for. It will be understood that if the lines be centered in a multiple switchboard they will be provided with any suitable and usual test system, and connection will 5 be made with a spring-jack only after a process of testing the line called for to determine whether it be already in use. Having made connection with the line called for, the operator will work the key 9 to ring the bell at IO the called station, after which she will disconnect her telephone from the circuit. The insertion of plug f into the spring-jack b of line to station A completes circuits from the conductors 7 and 8 of the plug-circuit to the line conductors 1 and 2, respectively, of the line. A path is thus furnished from battery 6 through wire 6 to line conductors 1 and 2, thence through the spring-jack and plug to the conductors 7 and 8 of the plug-circuit, and from theseto the wire 9 to earth, and there is also a path over the line conductors 1 and 2 to the called substation, and thence to earth through wire 5, which being of much lower resistance than that througli the clearing-out annunciator shunts the latter instrument and renders its magnet inert. Hence the placing of the plug f in the spring-jack of the line called brings the target of the clearing-out indicator into view to show the 0 operator that the telephone at the called. station remains on its switch, When the called subscriber responds to the signal and removes his telephone from the switch, breaking the wire 5, the current of battery e in the outgo- 5 ing line-circuit is broken, and the current flowing through signal 41 becomes sufficient to conceal the indicator thereof. The disappearance of this indicator is therefore a sig nal to the operator that the called party has answered the call. We have indicated the subscribers telephone talking apparatus at the substation ina diagrammatic way without.

showing in detail the usual induction-coiland the local-battery circuit for supplying our- 5 rent to the subscribers microphone, since such apparatus is well known in the art and constitutes no part of this invention. It will be understood, of course, that any suitable telephone talking apparatus of this character may be provided; but in order that the drawing may be considered as illustrating on its face an operative system the telephone-transmitter may be considered as of the magneto type, in which no battery is employed, or the diagrammatic illustration of the transmitter may be understood as comprehending the usual induction-coil and local-battery circuit in addition to the microphone itself. When conversation between correspondents is finished and both telephones are replaced on their switches, the conductors 5 at both stations are completed, and the clearing-out signal is again shunted and displays its indica- V tor. This second display of the indicator is a call for disconnection and is followed by the removal of plugs f and f from the springjacks and their replacement in their resting places.

What we claim is 1. In combination, a telephone-line, a linesignal therefor connected with the line, a source of current in circuit with the line-signal, the signal being adapted to display its indicator when inert, and means controlled from the substation for rendering the signal inert; plugs and a plug-circuit for making connection with the line, and a clearing-out signal associated with the plug-circuit and in connection therewith, the clearing-out signal being adapted to display its indicator when inert; circuit connections adapted to complete a local circuit when the plug-circuit is con nected with the line, said local circuit including the source of current, the line-signal and the clearing-out signal; and means controlled from the substation adapted to break the current through the clearing-out signal; whereby the line-signal and the clearing-out signal are concealed in making connection with the line, while the clearing-out signal may be controlled from the substation of the line, as described.

2. In combination,a telephone-line,a switch for closing a return-circuit thereto at the substation, and a line-signal and a source of current in a permanent connection between the said line and the said return-circuit at a central station, the said signal being adapted to display its indicator when inert; a plug and a plug-circuit for making connection with the line and a clearing-out signal in a branch be tween said plug-circuit and said return-eir cuit, said clearing-out signal being adapted to display itsindicator when inert; and means at the substation for diverting current from the said clearing-out signal to permitits dis play, substantially as described.

3. In combination, a metallic-circuit telephone-line, a bridge of the line at the sub station, a telephone -switch, and a ground branch from said bridge controlled by the switch, a bridge of the line at the central ofiice having impedance-coils interposed therein, a ground branch from the said bridge, a source of current in the said branch and a line-Sig; nal connected with the line to be in the path of current from said source; a spring-jack for the line, a plug and a plug-circuit for making connection therewith,a bridge of the plugcircuit including impedance, and a ground branch from the said bridge; both of said signals being adapted to display their indicators when inert, and the circuit through said clearing-out signal being of high resistance compared to that of the circuit through the line to earth at the substation; whereby making connection with the line causes the concealment of the line-signal and the clearingout signal, while placing the telephone on its switch at the substation during connection displays the clearing-out signal, as described.

4. The combination with telephone-lines,

plugs and a plug-circuit for uniting lines, a bridge of the plug-circuit, a clearing-out signal in the bridge, the signal being adapted to display its indicator when its magnet is inert, a source of current in circuit with the clearingout signal, and means controlled.

5. In combination, a metallic-circuit telephone-line, a bridge of the line at the substation, a call-bell in the said bridge, and a ground branch from the middle of said callbell, a bridge of the line at the central office,

two impedance-coils in the said bridge, a ground branch from the said bridge between the said impedance-coils, and a line-signal andsource of current in the ground branch,

said signal being adapted to display its indicator when inert; plugs and a plug-circuit for making connection between lines, a bridge of the plug-circuit, impedance-coils .in the bridge, a ground branch from the bridge be tween the impedance-coils, and a clearingout signal in the ground branch, the clearing-out signal being adapted to display its indicator when inert, said clearing-out indicator being of high resistance; a plug-seat switch for one of said plugs, and a local circuit, including a source of current, together with said clearing-out signal, normally completed in the switch-contacts of said plugseat switch, as described.

Signed at Glasgow, Scotland, this 17th day of December, 1897.

DANIEL SINCLAIR. WILLIAM AITKEN. 

